Field of the Invention
This disclosure relates to night vision imaging systems (NVIS), and particularly to liquid crystal displays (LCD) for use with night vision imaging systems.
Description of Related Art
Pilot-aircraft interface is a major component of aerospace design. A pilot must be able to quickly determine flight critical information such as, but not limited to, location, altitude, engine status, and fuel level. This is especially true for pilots flying aircraft which not only face extreme conditions but that have additional situational awareness requirements that require the pilot's attention during night missions while wearing night vision goggles. Such requirements include, but are not limited to, weapon systems management, search and rescue and safety concerns relating to the constant awareness of other aircraft.
Liquid crystal displays (LCD), such as active-matrix liquid crystal displays (AMLCD), provide excellent image quality and low power consumption while being thin and lightweight. In light of these advantages the LCD has become a preferred display device used in specialized civil and military aircrafts. During flight operation at night, LCDs are used with night vision imaging systems (NVIS). Pilots wear near infrared sensitive NVIS goggles which allow them to maintain proper night vision sensitivity. However, conventional LCD devices emit energy in the NVIS sensitive region, which causes near infrared sensitive goggles to “bloom,” greatly reducing their effectiveness. To use NVIS systems during nighttime operations, the cockpit LCD devices must be compatible with NVIS systems.
Currently there are two employed strategies to achieve NVIS compatibility for an LCD device. One approach involves the use of an NVIS backlight together with a normal mode backlight and provides a dual mode display. Such dual mode NVIS displays have high manufacturing costs associated with the production and assembly of a complex backlight panel.
Another common strategy is to use an external NVIS filter that blocks red and near-infrared radiation from a normal mode backlight. These include NVIS absorptive glass, thin film dichroic coatings and NVIS polymeric filters. An NVIS filter can be mounted on either of the two surfaces of an LCD panel (front or rear). Such filters are costly and add to the face height of a display device. Also, the conventional absorptive NVIS filters have low visible light transmission (VLT) of less than 30% and cut the red from the color spectrum limiting the displays color gamut. These NVIS filters often have to be disassembled from a display during daylight operation due to low luminance and reduced color purity of the display.
Accordingly, a desire exists for an inexpensive NVIS solution for an LCD display that provides NVIS compatibility, does not interfere with full color LCD performance, and does not reduce luminance of a display. Further, an NVIS solution that does not require the introduction of structural modifications to the LCD device assembly or the addition to the total thickness of the LCD device can be beneficial.